Log verbosity configuration

[regressEdo]

Description

Hello,

Is it possible to tune the log verbosity? I could only find a way to enable debug and trace but I could not find a way to remove info logs for example and so be able to only log from warning up

Thanks

[crazy-max]

Maybe we could add a level attribute to log config https://github.com/moby/buildkit/blob/15b43c86133070a488ee44f868a576ebcb7fe4b8/cmd/buildkitd/config/config.go#L57-L59

And deprecate debug and trace attributes.

We might keep --debug and --trace flags as shorthand for --log-level flag.